C++ code reduction for identical submenus - c++

Question

I am coding my way to the last project of the semester and I have a code duplication issue.
I am using ncurses or pdcurses to make a menu to interact with the user.
The problem: For each choice of the menu(Five in total) I need a submenu. The submenu's only difference from the main menu is, the array of Items to be printed, and the parameters that go into some functions, as a result of the Items array size. Since I need five submenus, I need five times the same code(six if you add the main menu).
Could any of you help me make a function that does the same thing, which I'll then call six times to create my menu?
Here's my code
void Menu(){
const char* Items[]={
"[1]...New tax declaration",
"[2]...Modify tax declaration",
"[3]...Cancel tax declaration",
"[4]...Additional Information",
"[5]...Exit"
};
int Cur=0;
int ch, i;
int flag=0;
do{
werase(wm);
mvwaddstr(wm, 2, 16, "MENU");
for(int i=0; i<5;i++){
if(i==Cur)
wattr_on(wm, A_REVERSE, 0);
mvwaddstr(wm, 4+i, 4, Items[i]);
wattr_off(wm, A_REVERSE, 0);
}
mvwaddstr(wm, 14, 3, "Choice: ");
wprintw(wm, "%1d", Cur+1);
wrefresh(wm);
ch=wgetch(wm);
switch(ch){
case '1':Cur=0;Sub2();break;
case '2':Cur=1;Sub1();break;
case '3':Cur=2;break;
case '4':Cur=3;break;
case '5':flag=1;break;
case KEY_UP:
case KEY_LEFT: Cur--; if (Cur<0) Cur=4; break;
case KEY_DOWN:
case KEY_RIGHT: Cur++; if(Cur>4) Cur=0; break;
case 27: flag=1; break;
case 32:
case 13:
switch (Cur){
case 0:Sub2();break;
case 1:Sub1();break;
case 2:break;
case 3:break;
case 4:flag=1;break;
}
}
}while(!flag);
}
Thank you.
p.s The code is from a book. I have little experience with ncurses

Answer 1

A simple menu-driven program. This is based on using std::map instead of conditional logic. This map stores a list of menuitem structures that define what the menu looks like and what each option does.
This is best explained as we work through the code, so let's dive in!
// headers for everything used in this example
#include <iostream>
#include <string>
#include <map>
#include <functional>
#include <cctype>
// function to perform menu option B sub option 1
void optionB1()
{
std::cout << "perfoming B1" << std::endl;
}
// function to perform menu option B sub option 2
void optionB2()
{
std::cout << "perfoming B2" << std::endl;
}
// function to perform menu option A
void optionA()
{
std::cout << "perfoming A" << std::endl;
}
// defines a menu item. Good naming can often save the need to comment
struct menuitem
{
std::function<void()> doIt; // function to run if option chosen
std::string description; // pretty message describing option
};
// draw menu and wait for the user to select an option.
void domenu(const std::map<char, menuitem> & menu)
{
while (true) // loop until user gives a good option. Or use a retry count.
// You decide.
{
for (auto &items : menu)
{ // for all items in the menu, print out the item and it's description text
// for what first and second mean, read up on std::map and std::pair
std::cout << items.first << ") " << items.second.description << std::endl;
}
char ch;
std::cin >> ch; // get the user's choice
// often you may want to eliminate one of the cases to reduce the amount
// of possible inputs you need to provide handling code for.
// the line below allows us to use the same code for input of A and a.
ch = std::tolower(ch); // convert input to lower case
try
{
menu.at(ch).doIt(); // call the function mapped to user's choice.
// this may do produce something or it may
// display another menu. It could end the wor--
return; // done.
}
catch (...)
{ // print error message on unsupported input
std::cout << "Error. Invalid option!" << std::endl;
}
}
}
// the B menu
std::map<char, menuitem> bmenu
{ // User input doIt function Description
{'1', {optionB1, "Option B1"}},
{'2', {optionB2, "Option B2"}}
// add more options here. Or don't. Up to you.
};
// the main menu
std::map<char, menuitem> mainmenu
{ // User input doIt function Description
{'a', {optionA, "Option A"}},
{'b', {std::bind(domenu, bmenu), "Option B"}}
// OK, so that last one was a bit weird. std::bind makes a function and
// specifies the arguments with which it will be called. This takes
// domenu binds it with bmenu so that std::function<void()> is
// satisfied. As far as the world is concerned, the bound function
// returns nothing and takes no parameters. Very complicated functions
// can be bound so long as the end result returns nothing and requires
// no parameters.
// what it's doing here is allowing us to call domenu to draw the B
// submenu, wait for valid input, and call the chosen function.
};
// good 'ol trusty main so we can test that the above code isn't utter BS.
int main()
{
while (true) // loop forever. Or use whatever exit logic is required.
{
domenu(mainmenu); // kick-start by calling do menu to run the main menu
}
return(0);
}
This will keep the code down to a minimum. All of the duplicated code is reduced to the domenu function and a smurfload of code hidden from sight in the standard library and written by folks who likely have far more experience in getting this stuff right than you or I. Whenever possible, stand on the shoulders of giants.
domenu is driven by lists of options and execution instructions for the option. Want another option? Add an item to a list and possibly provide a new function to fulfill the obligations of that option.
All you have to do is fill in the blanks.